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The temporal evolution of fluorescence intensity of a single blinking CdSe/ZnS nanocrystal (quantum dot, QD) has been measured with continuous wave (CW) laser excitation at room temperature. Tracks exhibit ON-/OFFfluctuations with large amplitude and intensity fluctuations with small amplitude in the ON-interval. The QD photon distribution function was obtained by statistical analysis of this fluorescence track. The experimental QD photon distribution function was compared with an analogous function calculated with the Monte Carlo technique on the basis of two mechanisms for intermittency which take into account both ionization/neutralization processes in the QD core, as well as diffusive fluctuations of atoms on the core−shell interface. We show that a combined model based on these two mechanisms sufficiently describes the shape of the measured photon distribution function.

Distribution function w(N)(T) for photons created by three-level nanoparticle in time interval T under cw laser excitation is calculated for various methods of photon counting. It is found that each exponential process exp(-lambda(i)t) in quantum dynamics of three-level nanoparticle manifests itself via Poissonian function P(N)(lambda(i)t)=(lambda(i)t)(N) exp(-lambda(i)t)/N! in the photon distribution function w(N)(T). The distribution function w(N)(T) is expressed via two or three integrals of two or three Poissonian functions P(N)(lambda(i)t). The simple mathematical expression for w(N)(T) enables one to calculate photon distribution in blinking fluorescence with on and off intervals. A scaling between photon distribution function w(N)(T) and photoelectric pulse distribution function w(n)(T) is found. Comparison of the theoretical distribution w(n)(T) and the distribution measured in blinking fluorescence of single polymer molecule dPPV-PPyV and complex organic molecule 1,1(')-didodecyl-3,3,3('),3(')-tetramethylindocarbocyanine perchlorate (DiI) is carried out. The theoretical distributions are able to describe those found in an experiment.